An arrangement for the distribution of send or write permission to computers connected in a loop is described in an article by M. T. Liu and C. C. Reames, "The design of distributed computer network", Proc. Int. Computer Symp. 1975, Vol 1 pages 273-282. The article shows that by permitting a computer to send, i.e. to break the loop, on condition that no information frame is passing that moment, several terminals can send at the same time. Each computer is then prepared to receive incoming data, store the data in a buffer store and to return the data to the loop (Ref 1).
Another known device gives send permission by means of a special bit pattern. The bit pattern is converted or reshaped (retransmitted) depending on whether the send permission is accepted or refused. The device is presented in an article by W. D. Farmer and E. F. Newhall, Proc, ACM Symp. Probl. Optim. Data communication System 1-33, 1969 (Ref 2).